...Bob,I may be wrong here,but,isn't the grounded conductor considered current-carrying ONLY when used in circuits where there are non-linear loads harmonics,such as HID lighting,servo controls,ballasts,or in a 3 phase wye utilizing only 2 phases and a neutral...etc??otherwise,if the circuit is balanced,the current on the neutral is 0,you wouldn't count it as current -carrying for derating purposes,ampacity..??Russ

... Take a normal 3 phase wye circuit,..all sharing the neutral,and the loads close to being equal...(barring the use of HID fixtures,processors,variable speed drives etc)and you should have a balanced circuit..Russ